Turbulence, early

The preceding equations are reported to predict actual heat transfer coefficients only about 15% lower than experimental values—the difference can be attributed to the rippling of the film and early turbulence and drainage instabilities on the bottom side of the tube. ... 

Forame PC, Hansen RJ, Little RC (1972) Observations of early turbulence in the pipe flow of drag reducing polymer solutions AIChE J 18 213... 

Nonintrusive Instrumentation. Essential to quantitatively enlarging fundamental descriptions of flow patterns and flow regimes are localized nonintmsive measurements. Early investigators used time-averaged pressure traverses for holdups, and pilot tubes for velocity measurements. In the 1990s investigators use laser-Doppler and hot film anemometers, conductivity probes, and optical fibers to capture time-averaged turbulent fluctuations (39). 

Early models used a value for that remained constant throughout the day. However, measurements show that the deposition velocity increases during the day as surface heating increases atmospheric turbulence and hence diffusion, and plant stomatal activity increases (50—52). More recent models take this variation of into account. In one approach, the first step is to estimate the upper limit for in terms of the transport processes alone. This value is then modified to account for surface interaction, because the earth s surface is not a perfect sink for all pollutants. This method has led to what is referred to as the resistance model (52,53) that represents as the analogue of an electrical conductance... 

Computational fluid dynamics (CFD) is the numerical analysis of systems involving transport processes and solution by computer simulation. An early application of CFD (FLUENT) to predict flow within cooling crystallizers was made by Brown and Boysan (1987). Elementary equations that describe the conservation of mass, momentum and energy for fluid flow or heat transfer are solved for a number of sub regions of the flow field (Versteeg and Malalase-kera, 1995). Various commercial concerns provide ready-to-use CFD codes to perform this task and usually offer a choice of solution methods, model equations (for example turbulence models of turbulent flow) and visualization tools, as reviewed by Zauner (1999) below. 

A deflagration-detonation transition was first observed in 1985 in a large-scale experiment with an acetylene-air mixture (Moen et al. 1985). More recent investigations (McKay et al. 1988 and Moen et al. 1989) showing that initiation of detonation in a fuel-air mixture by a burning, turbulent, gas jet is possible, provided the jet is large enough. Early indications are that the diameter of the jet must exceed five times the critical tube diameter, that is approximately 65 times the cell size. 

The transition to turbulent flow occurred at Re of about 1,500. The authors noted that for smaller micro-channels, the flow transition would occur at lower Re. The early transition phenomenon might be affected by surface roughness and other factors. 

Lelea et al. (2004) investigated experimentally fluid flow in stainless steel microtubes with diameter of 100-500 pm at Re = 50-800. The obtained results for the Poiseuille number are in good agreement with the conventional theoretical value Po = 64. Early transition from laminar to turbulent flow was not observed within the studied range of Reynolds numbers. 

Because most applications for micro-channel heat sinks deal with liquids, most of the former studies were focused on micro-channel laminar flows. Several investigators obtained friction factors that were greater than those predicted by the standard theory for conventional size channels, and, as the diameter of the channels decreased, the deviation of the friction factor measurements from theory increased. The early transition to turbulence was also reported. These observations may have been due to the fact that the entrance effects were not appropriately accounted for. Losses from change in tube diameter, bends and tees must be determined and must be considered for any piping between the channel plenums and the pressure transducers. It is necessary to account for the loss coefficients associated with singlephase flow in micro-channels, which are comparable to those for large channels with the same area ratio. 

The knowledge of turbulent premixed flames has improved from this very simple level by following the progress made in experimental and numerical techniques as well as theoretical methods. Much employed in early research, the laboratory Bunsen burners are characterized by relatively low turbulence levels with flow properties that are not constant everywhere in the flame. To alleviate these restrictions, Karpov et al. [5] pioneered as early as in 1959 the studies of turbulent premixed flames initiated by a spark in a more intense turbulence, produced in a fan-stirred quasi-spherical vessel. Other experiments carried out among others by Talantov and his coworkers allowed to determine the so-called turbulent flame speed in a channel of square cross-section with significant levels of turbulence [6]. 

Paracelsus lived during the Renaissance. His sober spirit of scientific observation and critical reason were accompanied by emotional turbulence and a volcanic temperament. He remains both a mystery and an object of nostalgia. Paracelsus is today celebrated as the first modem medical scientist. Paracelsus early life, achievements and latter years are described... 

Entry page to Introduction and urls for 13 documents. "The Corpus Hermeticum are the core documents of the Hermetic tradition. Dating from early in the Christian era, they were mistakenly dated to a much earlier period by Church officials (and everyone else) up until the 15th century. Because of this, they were allowed to survive and we seen as an early precursor to what was to be Christianity. We know today that they were, in fact, from the early Christian era, and came out of the turbulent religious seas of Hellenic Egypt. 

Turbulent free convection attracted early attention in limiting-current studies, because the laminar, free convection boundary layer at a vertical plate becomes turbulent at a height characterized approximately by the Rayleigh number... 

Because the CA are well suited to the description of temporal phenomena, it will be no surprise that an early application of CA in science was in hydro-dynamic flow. Wolfram, who has been an enthusiastic advocate of CA, has used them successfully in the simulation of turbulent flow — a demanding area for simulations of any type. Indeed, Wolfram s work covers a range of topics in physics and uptake of the method among scientists owes much to his work.4... 

Usually, however, the stresses are modeled with the help of a single turbulent viscosity coefficient that presumes isotropic turbulent transport. In the RANS-approach, a turbulent or eddy viscosity coefficient, vt, covers the momentum transport by the full spectrum of turbulent scales (eddies). Frisch (1995) recollects that as early as 1870 Boussinesq stressed turbulence greatly increases viscosity and proposed an expression for the eddy viscosity. The eventual set of equations runs as... 

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